FBAR based duplexer device and manufacturing method thereof

ABSTRACT

Disclosed herein is an FBAR based duplexer device and a manufacturing method thereof, which can achieve miniaturization, and reduction of a manufacturing cost and enhancement of a yield due to a simplified process. According to the present invention, first, a plurality of FBAR chips are prepared. Each of the FBAR chips comprises a substrate, air gaps and piezoelectric layer unit, which are successively arranged, a plurality of electrode pads electrically connected to the piezoelectric layer unit, and bump balls formed on the electrode pads in a one to one ratio. Then, a duplexer substrate having a duplexing circuit is prepared, and a plurality of the FBAR chips come into contact with the duplexer substrate. In this state, they are reversed so that the substrates of the FBAR chips face upward, and the bump balls are bonded to the duplexer substrate. After that, protective structures are formed by the use of a film, so as to be positioned on side surfaces as well as upper surface of the respective FBAR chips, and finally, a molding portion is formed so as to cover the protective structures.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a duplexer device implemented by usinga film bulk acoustic resonator (hereinafter, referred to as an FBAR),and a manufacturing method thereof, and more particularly to an FBARbased duplexer device, and a manufacturing method thereof, which canachieve miniaturization, and reduction of a manufacturing cost andenhancement of a yield due to a simplified process.

2. Description of the Related Art

In recent years, wireless communication devices have tended to becomemuch leaner, and enhanced and diversified in their quality and functionsdue to the development of the communication industry. This recent trendsincerely requires miniaturization and enhancement in quality relatedwith various elements for use in the wireless communication devices.

In order to satisfy such requirements to miniaturization, therefore,currently, active development is targeting studies for manufacturingessential components of wireless communication devices, such as a filterand a duplexer, by using FBARs. The FBARs are preferable for integrationdue to their thin film shapes, and have good properties.

Typically, the FBARs are usually formed in such a fashion that apiezoelectric layer is formed on a wafer, and upper and lower electrodesare formed at the upper and lower surfaces of the piezoelectric layer,respectively, for applying electricity to the piezoelectric layer so asto induce oscillation thereof. Further, a desired air gap is formed atthe lower surface of the piezoelectric layer in order to improve aresonance property of the piezoelectric layer.

FIGS. 1A and 1B are sectional views, respectively, illustratingdifferent structures of conventional duplexer devices implemented byusing the FBARs formed as stated above.

The conventional FBAR based duplexer device shown in FIG. 1A comprisesat least two FBARs 12, mounted on a substrate 11 serving as a lowersupport, for forming a Tx (transmitter) filter and an Rx (receiver)filter, respectively. The substrate 11 is formed with a common terminaland transmission/receiving terminals, and circuit patterns forelectrically connecting the terminals to the Tx and Rx filtersimplemented by the FBARs. After the FBARs 12 are electrically connectedto the circuit patterns formed at the substrate 11, in order to achievea complete sealing of all of the FBARs 12, a molding portion 13 isformed on the substrate 11 by the use of certain sealing material.

As the substrate 11, due to the complexity of implemented circuitsthereof, printed circuit board (PCB) type or low temperature co-firedceramic (LTCC) type substrates are mainly used, but the PCB substratesare more preferable since they have many advantages, such as a lowprice, good properties and high productivity. In case of using the PCBsubstrates, as shown in FIG. 1A, it is necessary to provide certainprotective structures on the FBARs 12, respectively, for protectingdevice functional portions, that is, piezoelectric layers, air gaps, andelectrode layers, of the FBARs 12 from a molding process. Theseprotective structures may be formed, for example, by processing a waferhaving a certain thickness according to a wafer level package (WLP)technique, and bonding the processed wafer onto a substrate wafer of thecorresponding FBAR.

In case that the FBARs 12 are formed with the protective structures,respetively, as stated above, however, the overall structure andmanufacturing process of the FBARs 12 are disadvantageously complex,since the protective structures should be configured so as to beelectrically connected to the device functional portions inside theFBARs 12, respectively, as well as protect the device functionalportions.

When an FBAR is bonded to a substrate obtained by a wafer level packageprocess, the obtained wafer level package type FBAR device has a verysmall size of about 1 millimeter in length and width. Due to the smallsize, a cap and substrate constituting the package has a sealing areacorresponding to only about 30 to 100 square micrometers, with theexception of a driving portion. Since the FBAR device can endure onlyabout 30° C. during its bonding process, there is a considerablerestriction in a sealing method for securing a good reliability.

Even when a large amount of the FBAR devices are produced through anyprecision processes, due to a complexity in process thereof, it isdifficult to obtain an appropriate yield.

In case that an LTCC technique is adopted in order to eliminate theabove problems, as shown in FIG. 1B, first, a plurality of ceramicsheets are vertically laminated so as to form an LTCC substrate 15,which is defined therein with a cavity, and then a plurality of FBARs 16are mounted inside the cavity defined in the LTCC substrate 15. Afterelectrically connecting the FBARs 16 to the substrate 15 by bondingwires therebetween, a metal lead 17 is fused or seam-sealed on the LTCCsubstrate 15 above the FBARs 16.

In this case, since the LTCC substrate 15 is configured in such afashion that circuits having a duplexing function are arranged thereinin a multi-stage form, it is possible to achieve a reduction in size,compared with the case of using a single layer PCB substrate. Further,the LTCC substrate does not need a molding process. Furthermore,according to the structure of the LTCC substrate 15 as stated above, theLTCC substrate 15 already owns certain protective structures forprotecting the FBARs 16. The protective structures are side wallsobtained by defining the cavity in the substrate 15. Therefore, the LTCsubstrate 15 does not need separate protective structures. That is, theFBARs 16 only comprise an air gap, piezoelectric layer and electrodelayers vertically arranged in series on an FBAR substrate wafer.

The LTCC technique, however, causes torsion of the LTCC substrate 15during a LTCC firing process, resulting in a serious leak problem due toinferior bonding between the lead 17 and the LTCC substrate 15. Further,due to the fact that the LTCC substrate 15 is formed by verticallylaminating a plurality of the ceramic sheets, there is a highpossibility of producing any defects in the LTCC substrate itself.

Although the above techniques have been achieved according to a mosteffective method for miniaturization, since a possibility of inferioritydue to complex processes always exists, it is difficult to secure aprofit margin required for mass production, causing an unnecessarilyhigh manufacturing cost, and to increase a possibility of producinginferior products due to an operator's carelessness.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide anFBAR based duplexer device, and a manufacturing method thereof, whichcan achieve miniaturization, and reduction of a manufacturing cost andenhancement of a yield due to a simplified process.

In accordance with one aspect of the present invention, the above andother objects can be accomplished by the provision of a method formanufacturing an FBAR based duplexer device comprising the steps of: a)preparing a plurality of FBAR chips, each FBAR chip comprising asubstrate, air gap and piezoelectric layer unit, which are successivelyarranged, a plurality of electrode pads electrically connected to thepiezoelectric layer unit, and bump balls formed on the electrode pads ina one to one ratio; b) preparing a duplexer substrate having a duplexingcircuit; c) reversing a plurality of the FBAR chips after contactingthem with the duplexer substrate so that the substrates of the FBARchips face upward, and bonding the bump balls to the duplexer substrate;d) forming protective structures by the use of a film, the protectivestructures being positioned on side surfaces as well as an upper surfaceof the respective FBAR chips; and e) forming a molding portion on theduplexer substrate so as to cover the protective structures.

Preferably, the step a) may include the steps of: a-1) dividing an FBARchip substrate wafer into a plurality of wafer sections by the use ofvertical and horizontal lines, and forming a plurality of sacrificiallayer units on the divided wafer sections, respectively; a-2) formingthe piezoelectric layer units on the sacrificial layer units,respectively; a-3) forming a plurality of the electrode pads on eachwafer section, the electrode pads being electrically connected to thepiezoelectric layer unit of the corresponding wafer section; a-4)forming the air gaps by removing the sacrificial layer units; a-5)forming the bump balls on the electrode pads in a one to one ratio; anda-6) cutting the FBAR chip substrate wafer into the divided wafersections, thereby obtaining a plurality of the individual FBAR chips.

Preferably, the step d) may include the steps of: d-1) laminating a dryfilm on an overall surface of the duplexer substrate and hence the FBARchips; and d-2) removing unnecessary portions of the dry film laminatedon the duplexer substrate.

Preferably, the duplexer substrate may be made of PCB sheets.

Preferably, the dry film may be an insulation film including aphotosensitive polymer film or a non-photosensitive polymer film.

Preferably, the step d-2) may include the steps of: d-2-1) exposing theunnecessary portions of the dry film to be removed to a light, throughthe use of a mask; and d-2-2) removing the exposed portions of the dryfilm by simultaneously applying a chemical process using a developersolution and a physical process using high pressure dispensing.

In accordance with another aspect of the present invention, the aboveand other objects can be accomplished by the provision of an FRAR basedduplexer device comprising: a PCB substrate having a duplexing circuit;a plurality of FBAR chips, each comprising an FBAR chip substrate, anair gap defined at a lower surface of the FBAR chip substrate, apiezoelectric layer unit formed under the air gap, a plurality ofelectrode pads provided at a lower side of the FBAR chip substrate so asto be electrically connected to the piezoelectric layer unit, and aplurality of bump balls formed on a lower side of the electrode pads soas to be bonded to an upper surface of the PCB substrate; protectivestructures made of a film, the protective structures being laminated onthe PCB substrate so as to cover side surfaces and upper surfaces of therespective FBAR chips; and a molding portion formed on the PCB substrateso as to completely cover the protective structures.

Preferably, the protective structures may be made of an insulation filmincluding a photosensitive polymer film and a non-photosensitive polymerfilm, and laminated on the PCB substrate by using a vacuum deposition.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIGS. 1A and 1B are sectional views, respectively, illustratingconventional FBAR based duplexer devices;

FIG. 2 is a sectional view illustrating an FBAR based duplexer device inaccordance with the present invention;

FIG. 3 is a flow chart illustrating a method for manufacturing the FBARbased duplexer device in accordance with the present invention; and

FIGS. 4A and 4H are sectional views, respectively, illustrating thesequential steps of manufacturing the FBAR based duplexer device inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, an FBAR based duplexer device, and a manufacturing method thereofaccording to the present invention will be described, with reference tothe accompanying drawings.

As shown in FIG. 2 illustrating the sectional structure of the FBARbased duplexer device in accordance with the present invention, the FBARbased duplexer device of the present invention comprises a substrate 110serving as a lower support, a plurality of FBAR chips 120 mounted on thesubstrate 110 in a flip chip bonding manner and adapted to form Tx andRx filters, respectively, a plurality of protective structures, made offilms, for wholly covering the upper and side surfaces of the respectiveFBAR chips 120, and a molding portion 140 formed on the substrate 110 soas to enable the protective structures 130 to be completely covered. Thesubstrate 110 is formed with a common terminal andtransmission/receiving terminals and circuit patterns for electricallyconnecting the terminals to the Tx and Rx filters embodied by the FBARchips 120.

The substrate 110 may be freely selected from among various kinds ofsubstrates including a PCB substrate or LTCC substrate so long as itallows the formation of circuits thereon, however, it is more preferableto use the PCB substrate in view of cost or productivity. In particular,the PCB substrate may be formed by stacking a plurality of PCB sheets ina multi-layer structure, so that the respective sheets are regularlyarranged in vertical and horizontal lines.

Each of the FBAR chips 120 comprises a certain sized FBAR chip substrate121 defined at the bottom portion thereof with an air gap 122, apiezoelectric layer unit 123 formed at the lower surface of the FBARchip substrate 121 so as to be positioned under the air gap 122, aplurality of electrode pads 124 formed at the lower surface of the FBARchip substrate 121 and adapted to be electrically connected with thepiezoelectric layer unit 123 for performing input and output of signals,and a plurality of bump balls 125 formed at the lower side of theelectrode pads 124 in a one to one ratio. These bump balls 125 arebonded onto the substrate 110 of the FBAR based duplexer device.

That is, the FBAR chip 120 comprises the FBAR chip substrate 121, airgap 122, and piezoelectric layer unit 123, which are successivelyarranged. After the bump balls 125 are formed, respectively, at theelectrode pads 124, which are provided so as to be electricallyconnected to the piezoelectric layer unit 123, the FBAR chip 120 isreversed so that the FBAR chip substrate 121 is located at the uppermostposition. In this case, the FBAR chips 406 face upward, and thesubstrate 110 of the FBAR based duplexer device faces downward.

In this case, since the FBAR chip substrate 121 is located at theuppermost position, the FBAR chip substrate 121 can serve as an uppercover of the FBAR chip 120. Further, due to the bump balls 125 having acertain thickness, there exists a certain gap between the duplexersubstrate 110 and the piezoelectric layer unit 123 of the FBAR chip 120.

When it is desired to form the protective structure 130 by coating acertain dry film on the FBAR chip 120, which is mounted on the duplexersubstrate 110 in a flip chip bonding manner, the protective structure130 is adapted to be supported by the substrate 121 of the FBAR chip120. Therefore, since it is unnecessary to form separate side wallsaround the FBAR chip 120, the formation of the protective structure 130can be achieved with a single process.

The protective structure 130 is obtained by processing an insulationfilm selected from among various kinds of insulation films including aphotosensitive polymer film or a non-photosensitive polymer film. Sincethe protective structure 130 is molded and processed according togeneral thin-film processes including laminating, light-exposure,developing, hardening, and the like, it is possible to achieve precisionprocessing thereof, and to simplify its overall manufacturing processcompared with a wafer level package thus reducing the rate of generationof inferior products. Further, in comparison with the wafer levelpackage having a complexity in its manufacturing process, a yield andproductivity thereof are improved while an overall manufacturing cost isreduced. Furthermore, by additionally performing an ultraviolet exposureprocess in a state wherein a certain insulation film is coated on theFBAR chip 120, it is possible to increase the overall strength thereof.

The molding portion 140 of the FBAR based duplexer device is obtained byapplying a sealing material and the like on the duplexer substrate 110so as to completely cover all of the FBAR chips 120, and hardening theapplied sealing material.

As stated above, since the FBAR chip of the present invention comprisesa certain protective space for securing the normal function of thepiezoelectric layer unit 123 and the like by virtue of the thickness ofthe bump balls 125, and the protective structure 130, made of aninsulation film, seals the certain protective space from the outside,the FBAR chip 120 can be protected from any external stimulationsgenerated during the formation of the molding portion 140.

FIG. 3 is a flow chart illustrating a method for manufacturing the FBARbased duplexer device in accordance with the present invention.

FIGS. 4A and 4H are sectional views, respectively, illustrating thesequential steps of manufacturing the FBAR based duplexer device inaccordance with an embodiment of the present invention.

Now, a manufacturing method of the FBAR based duplexer device inaccordance with the present invention will be explained with referenceto FIGS. 3, and 4A to 4H.

For manufacturing the FBAR based duplexer device of the presentinvention, first, there is provided an FBAR chip wafer comprising aplurality of air gaps, piezoelectric layer units, and electrode pads,which are arranged at regular distances (step 301).

Referring to FIG. 4A, the FBAR chip wafer, designated as referencenumeral 401, is formed with air gaps 402, piezoelectric layer units 403,and electrode pads 404. These air gaps 402, piezoelectric layer units403, and electrode pads 404 can be formed by using various knownmethods. For example, an FBAR chip wafer having a certain area is firstdivided into a plurality of wafer sections by the use of vertical andhorizontal lines, and the respective wafer sections are formed withsacrificial layer units, respectively. Then, piezoelectric layer unitsare formed on the sacrificial layer units, respectively, andsubsequently a plurality of electrode pads are formed on each wafersection so as to be electrically connected to the piezoelectric layerunit provided on the wafer section. After that, the sacrificial layerunits are removed so as to form air gaps, which are vertically alignedwith the piezoelectric layer units.

Referring to FIG. 4B, on the electrode pads 404 of the FBAR chip wafer401 are formed bump balls 405, respectively (step 302).

As can be seen from the above description, the formation of the bumpballs 405 at the level of the FBAR chip wafer 401 can be achievedthrough a single process, regardless of the number of the FBAR chips.This is more advantageous than a conventional method wherein the bumpballs are formed at individual FBAR chips, respectively.

After that, as shown in FIG. 4C, the FBAR chip wafer 401, which isformed with the air gaps 402, piezoelectric layer units 403, electrodepads 404 and bump balls 405, is cut along predetermined vertical andhorizontal cutting lines as boundary lines between the divided wafersections, thereby forming a plurality of individual FBAR chips 406 (step303).

When a plurality of the FBAR chips 406 having a desired resonanceproperty are prepared according to the above steps 301 to 303, the FBARchips 406 are reversed at their original positions, thereby allowingtheir bump balls 405 to. be bonded to a duplexer substrate 407 (step304). In this state, the bump balls 405 of the FBAR chips 406 facedownward, and their FBAR chip wafers 401 face upward. FIG. 4Dillustrates the FBAR chips 406 bonded to the duplexer substrate 407 in aflip chip bonding manner.

Upon completion of such flip chip bonding, as shown in FIG. 4E, a dryfilm 408 is laminated over the duplexer substrate 407 and hence aplurality of the FBAR chips 406 (step 305). In this case, as thelaminating process is performed by the use of a vacuum laminator, thedry film 408 can be coated over the side surfaces as well as uppersurfaces of the FBAR chips 406.

Then, as shown in FIG. 4F, certain portions of the laminated dry film408, located on the duplexer substrate 407, are removed so as to exposeportions of the electrode pads 404 to the outside, through the use of amask (step 306). In this case, for the removal of the exposed portionsof the dry film 408, a chemical process using a developer solution and aphysical process using a high pressure dispensing may be simultaneouslyapplied.

The duplexer substrate 407 undergoes a dicing process as shown in FIG.4G, thereby achieving the removal of any frequencies and other factorseffecting properties of a resultant duplexer device. Subsequently, theduplexer substrate 407 is exposed to ultraviolet rays, so as to allow afilm 409 laminated thereon to be hardened (step 307).

Finally, as a certain sealing material is molded and hardened on thediced duplexer substrate 407, the FBAR based duplexer device packaged asshown in FIG. 4H is manufactured (step 308).

As apparent from the above description, the present invention providesan FBAR chip comprising a protective space via the use of a dry film anda flip chip bonding manner, resulting in an enhancement in a sealingdegree compared with conventional techniques. Further, according to thepresent invention, the FBAR chip comprises a protective structure, whichis configured in such a fashion that its side surfaces and upper surfaceare simultaneously formed with a single process, thereby achieving asimplification in a manufacturing process thereof thus increasing ayield while reducing overall manufacturing cost.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1-6. (canceled)
 7. An FBAR based duplexer device comprising: a PCBsubstrate having a duplexing circuit; a plurality of FBAR chips, eachcomprising an FBAR chip substrate, an air gap defined at a lower surfaceof the FBAR chip substrate, a piezoelectric layer unit formed under theair gap, a plurality of electrode pads provided at a lower side of theFBAR chip substrate so as to be electrically connected to thepiezoelectric layer unit, and a plurality of bump balls formed on alower side of the electrode pads so as to be bonded to an upper surfaceof the PCB substrate; protective structures made of a film, theprotective structures being laminated on the PCB substrate so as tocover side surfaces and upper surfaces of the respective FBAR chips; anda molding portion formed on the PCB substrate so as to completely coverthe protective structures.
 8. The device as set forth in claim 7,wherein the protective structures are made of an insulation filmincluding a photosensitive polymer film and a non-photosensitive polymerfilm, and laminated on the PCB substrate by using a vacuum deposition.